The mechanical and statistical behaviour of aerospace structural adhesives has been investigated by performing tensile tests on moulded samples and applying Weibull theory to results. Effects of loading rate, sample size and process parameters have been studied. The experimental design method has been employed in an attempt to extend the experimental results to other combinations of parameters. Three kinds of structural adhesive have been characterised, viz, Hysol((R)) EA9321, Hysol((R)) EA9394 and Hysol((R)) EA9395, which are particle reinforced epoxy adhesives, all of them containing voids with statistically distributed sizes (partially dependent on bonding technique). These highly heterogeneous, but natural, microstructures explain the dispersion of measured strength and Young's modulus of the materials. These two quantities are demonstrated not to be correlated. With these results, simple fibre bundle theory is used to evaluate the mean value and variance of the failure stress of a bonded joint loaded in tension.